Observation device and method of observing

Provided is an observation device and a method of observing capable of clearly obtaining information relating to a boundary part where a medium inside an observation object changes. An observation device (1) is a device for observing an observation object (2) including a sensitivity factor in which a dipole moment changes by sensing an electromagnetic wave (31). An output part (11) outputs the electromagnetic wave (31) and the dipole moment of the sensitivity factor included in the observation object (2) is changed by the electromagnetic wave (31). A detector part (12) detects, of the electromagnetic wave (31) outputted from the output part (11), a signal electromagnetic wave (33) which comes through the observation object (2) and a reference electromagnetic wave (32) which bypasses the observation object (2). A control part (13) analyzes the structure of the observation object (2) based on the detection results of the detection part (12). The electromagnetic wave (31) is pulse laser light which is intermittently outputted in pulse waveform. The wavelength of the electromagnetic wave (31) is arranged within the wavelength absorption band of the sensitivity factor.